(Z)-3-({[3-Methoxy-5-(trifluoromethyl)phenyl]imino}methyl)benzene-1,2-diol

The molecule of the compound adopts the phenol–imine tautomeric form. In the crystal, molecules are linked via pairs of bifurcated O—H⋯O hydrogen bonds between the phenol OH groups, forming inversion dimers with an (5) ring motif.

The title compound, C 15 H 12 F 3 NO 3 , crystallizes with one molecule in the asymmetric unit. The mean planes of the two phenyl rings of the Schiff base moiety, bearing the OH groups and the imine group, respectively, are inclined to each other by 4.91 (1) . In the crystal, molecules are linked via pairs of bifurcated O-HÁ Á ÁO hydrogen bonds between the phenol OH groups, forming inversion dimers with an R 1 2 (5) ring motif. The structure exhibits also intramolecular O-HÁ Á ÁN and C-HÁ Á ÁF hydrogen-bonding interactions. Hirshfeld surfaces analysis and two-dimensional fingerprint plots were applied to quantify the intermolecular interactions. The three F atoms of the trifluoromethyl group are disordered over two sets of sites, with occupancy factors of 0.578 (8) and 0.422 (8). The crystal studied was refined as an inversion twin 1. Chemical context Schiff bases (azomethines, imines) belong to a widely used group of organic compounds or intermediates that are important for production of certain chemical specialties, e.g. pharmaceuticals, or additives to rubber. The synthesis involves an aromatic amine and an aldehyde (Schiff et al., 1881). Schiff bases are also employed as catalyst carriers (Grigoras et al., 2001), thermo-stable materials (Vančo et al., 2004), metalcation complexing agents or in biological systems (Taggi et al., 2002). Furthermore, they are used as starting materials in the synthesis of significant drugs with properties such as antifungal, antibacterial, antimalarial, antiproliferative, antiinflammatory, antiviral, and antipyretic (Hadjoudis et al., 1987). On an industrial scale, they have a wide range of applications such as dyes and pigments.

Structural commentary
The title compound crystallizes as the phenol-imine tautomer with one molecule in the asymmetric unit (Fig. 1). The two ISSN 2056-9890 phenyl rings of the Schiff base (C1-C6 and C8-C13) are inclined at an angle of 4.91 (1) with respect to one another. The orientation of the two hydroxy groups with respect to their tautomeric counterparts is defined by the torsion angles T1(C1-C6-C7-N1) and T2(C7-N1-C8-C9). The respective values of = 2.0 (10) and À5.5 (11) indicate that the molecule is not planar (Ü nver et al., 2016).
In the molecule, the C N group has a strong electronwithdrawing character as revealed by the double-bond character of N1 C7 [1.269 (8) Å ] and the single bond character of O1-C2 [1.368 (6) Å ] in the phenol-imine tautomer. These values and other bond lengths and angles (Table 1) are in good agreement with those previously reported for C N and O-C bonds (Koşar et al.., 2010;Demir Kanmazalp et al.., 2019). One of the hydroxy groups (O2) makes a strong intramolecular O-HÁ Á ÁN bond to the imine N atom (Fig. 1, Table 2) with an S(6) ring motif, characteristic of o-hydroxysalicylidene systems. Other intramolecular hydrogen bonding interactions involve the disordered -CF 3 group and adjacent aromatic H atoms bonded to C9 and C11 ( Table 2). As a result of the strongly bent C-HÁ Á ÁF angles of about 100 , these contributions are of minor importance.

Figure 1
The molecular structure of the title compound with the atomic numbering scheme. The dashed line shows the intramolecular O-HÁ Á ÁN hydrogen bond. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Unit-cell packing diagram for the title compound. Intra-and intermolecular hydrogen bonds are shown as dashed lines. [Symmetry code: (i) Àx À 1, Ày, z À 1 2 .] (2) Å . The molecular conformations of these structures are also not planar, with dihedral angles between the phenyl rings varying between 5.00 (5) and 47.62 (9) . It is likely that the intramolecular O-HÁ Á ÁN hydrogen bond, where the imine N atom acts as an hydrogen-bond acceptor, is an important prere-quisite for the tautomeric shift toward the phenol-imine form.

Database survey
In fact, in all eight structures of the phenol-imine tautomers, hydrogen bonds of this type are observed.

Hirshfeld surface analysis
Hirshfeld surface analysis of the title compound was performed utilizing the CrystalExplorer program (Turner et al., 2017). The three-dimensional d norm surface is a useful tool for analysing and visualizing the intermolecular interactions and utilizes the function of the normalized distances d e and d i , where d e and d i are the distances from a given point on the surface to the nearest atom outside and inside, respectively. The blue, white and red colour convention used for the d normmapped Hirshfeld surfaces indicates the interatomic contacts longer, equal to or shorter than the van der Waals separations. The standard-resolution molecular 3D (d norm ) plot with d e and d i for the title compound is shown in Fig. 3. The bright-red spots near the oxygen and hydrogen atoms indicate donors and acceptors of a potential O-HÁ Á ÁO interaction. As can be seen from the two-dimensional fingerprint plots (scattering points spread up to d e = d i = 1.5 Å ; Fig. 4 View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm (in the range À0.211 to 1.077 a.u.), d e and d i .

Figure 4
Two-dimensional fingerprint plots of the crystal with the relative contributions of the atom pairs to the Hirshfeld surface.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The carbon-bound H atoms were positioned with idealized geometry and refined isotropically with C-H distances of 0.93-0.96 Å and U iso (H) set to 1.2-1.5U eq (C), and with O-H = 0.82 Å and U iso (H) = 1.5U eq (O).
The three F atoms of the trifluoromethyl group are disordered over two sets of sites, with occupancy factors of 0.578 (8) for F atoms with suffix A and 0.422 (8) for those with suffix B (Fig. 1). A similar behaviour for a disordered -CF 3 group was observed in a previous study (Demir et al., 2006). Restraints (SIMU, DELU and ISOR; Sheldrick et al., 2015b) were finally applied to the disordered trifluoromethyl group. As a result of missing anomalous dispersion, the absolute structure of the title compound could not be determined reliably (Table 3). Hirshfeld surface mapped over d norm to visualize the intermolecular interactions.   (Macrae et al., 2006); software used to prepare material for publication: SHELXL2018 (Sheldrick, 2015b), WinGX (Farrugia, 2012) and PLATON (Spek, 2009).

(Z)-3-({[3-Methoxy-5-(trifluoromethyl)phenyl]imino}methyl)benzene-1,2-diol
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refined as a 2-component inversion twin.